springmvc的ModelAttribute引文（转）_VC/MFC

springmvc的ModelAttribute注解（转）

参考资料:spring-framework-reference的Using @ModelAttribute on a method和Using @ModelAttribute on a method argument

[java]?view plain
@RequestMapping("/save")??
public?String?save(User?user)?{??
????user.setUsername("U?love?me");??
????userService.save(user);??
????return?"result";??
}??

其中User包含id和username两个私有属性,含有公共setter和getter方法.
执行此方法时会将key为"user"(注意:这里即使参数名称是user1,key一样还是"user"),value为user的对象加入到model.在jsp页面可以通过${user.id}和${user.name}得到值的,即上面方法和下面方法是相当的.

[java]?view plain
@RequestMapping("/save")??
public?String?save(Model?model,int?id,String?username)?{??
????User?user=new?User();??
????//这里是通过反射从request里面拿值再set到user??
????user.setId(id);??
????user.setUsername(username);??
????model.addAttribute("user",user);??
??????
????user.setUsername("U?love?me");??
????userService.save(user);??
????return?"result";??
}??

[email protected]
[email protected]

[java]?view plain
@ModelAttribute("user1")??
public?User?addUser(User?user)?{??
????return?new?User(520,"I?love?U");??
}??

假设此方法是写在UserController内,[email protected],[email protected]?加两个对象到model,先将key为"user"的对象(由addUser方法的User user引起的),再添加key为"user1"的对象([email protected]("user1")引起的).

[email protected]

[java]?view plain
@RequestMapping("/save")??
public?String?save(@ModelAttribute?User?user)?{??
????user.setUsername("U?love?me");??
????userService.save(user);??
????return?"result";??
}??

此方法会先从model去获取key为"user"的对象,如果获取不到会通过反射实例化一个User对象,再从request里面拿值set到这个对象,然后把这个User对象添加到model(其中key为"user").
[email protected],不一定是"user",此情况下,[email protected]

[email protected]ute,即上面两步的两个方法都添加UserController,如下:

[java]?view plain
@ModelAttribute("user1")??
public?User?addUser(User?user)?{??
????return?new?User(520,"I?love?U");??
}??
@RequestMapping("/save")??
public?String?save(@ModelAttribute?User?user)?{??
????user.setUsername("U?love?me");??
????userService.save(user);??
????return?"result";??
}??

假设要执行保存用户操作,根据一分析可知,先执行完会产生两个User类型的对象(一个key是"user",另一个key是"user1")添加到model,再执行save方法,此时会先从model去找key为"user"的对象,能找到再从request取值set到这个User对象.最后返回到jsp页面,model里也只有两个User类型对象.
再来个小小假设,[email protected]("user1")的user1改为user,其它不变.虽然执行了addUser方法,那么执行到save方法内,user对象的字段值还是来源于请求,最后返回到jsp页面,model里也只有一个User类型对象.

4.另类:

[java]?view plain
@ModelAttribute??
@RequestMapping("/save")??
public?String?save(@ModelAttribute?User?user)?{??
????user.setUsername("U?love?me");??
????userService.save(user);??
????return?"result";??
}??

此种情况,会添加一个key为"user"的User对象到model,还会添加一个key为"string",value为"result"的对象到model,而视图名称则变为了"save"而不是"result".相信一般开发者都不会这样用.

[email protected]

1.先看看这段代码

[java]?view plain
@Controller??
@RequestMapping("user")??
@SessionAttributes("test")??
public?class?UserController?{??
????@RequestMapping(value?=?"test1")??
????public?String?test1(Map<String,?Object>?model,?SessionStatus?sessionStatus)?{??
????????model.put("test","something");??
????????//sessionStatus.setComplete();??
????????return?"user/list";??
????}??
??
????@RequestMapping(value?=?"test2")??
????public?String?test2(Map<String,?>??model)?{??
????????Object?test?=?model.get("test");??
????????System.out.println(test);??
????????return?"user/list";??
????}??
}??

[email protected]("test"),它的作用是在controller共享 model 属性,直到调用org.springframework.web.bind.support.SessionStatus#setComplete会清除此session值.否则长期保留.因此先调用/user/test1,再调用/user/test2.在test2方法能得到test1方法put进去的值.当移除上面的注解,因为属性为test的session也被清除了,所以test2方法会得到是null.

[email protected]

[java]?view plain
@Controller??
@RequestMapping("user")??
@SessionAttributes("test")??
public?class?UserController?{??
????@RequestMapping(value?=?"test1")??
????public?String?test1(HttpServletRequest?request)?{??
????????User?user?=?new?User("xiejx618");??
????????request.getSession().setAttribute("test",user);??
????????return?"user/list";??
????}??
????@RequestMapping(value?=?"test2")??
????public?String?test2(@ModelAttribute("test")?User?user,SessionStatus?sessionStatus)?{??
????????System.out.println(user.getUsername());??
????????sessionStatus.setComplete();??
????????return?"user/list";??
????}??
}??

一样先调用/user/test1,再调用/user/test2.在test2方法能得到test1方法set进去的[email protected],[email protected],那么此方法会确保属性test的session会存在,否则会抛org.springframework.web.HttpSessionRequiredException异常,即上面代码先不调/user/test1,直接调/user/test2就会抛此异常

我个人很少这样用,用原始的写法就清晰很多了,但要看明白别人写的代码。